Omnidirectional antenna using dipoles



March 31, 1959 w. STOHR 2,880,418

OMNIDIRECTIONAL ANTENNA USING DIPOLES Filed Feb. 20. 1953 I3 N 2| l6wrfq 7 I9 24 6 l8 FIG.|

IN VENTOR WALTER sT6HR ATTORNEY United States Patent OMNIDIRECTIONALANTENNA USING DIPOLES Walter Stiihr, Berlin-Siemensstadt, Germany,assignor to Siemens & Halske Aktiengesellschaft, Munich, Germany, acorporation of Germany Application February 20, 1953, Serial No. 338,057

Claims priority, application Germany March 3, 1952 2 Claims. (Cl.343-799) This invention relates to antennae systems and is particularlyconcerned with an omnidirectional antenna.

In the case of an omnidirectional antenna comprising dipoles withreflectors which radiate in four main directions displaced by 90, therewill be observed in its radiation diagram more or less pronouncedextended radiations outside of the main radiation directions. Themagnitude of such extended radiations depends, in the presence ofsuitable relationship of the diameter of the mast or tower to wavelengthto be radiated, on the concentration characteristics of the individualdipoles. For example, by using half wave dipoles more energy will beradiated at an angle of 45 to the main radiation direction than in themain radiation direction. By using full wave dipoles, the energyradiated at each angle in the intermediate zones between the four mainradiation directions will be smaller than in each of the main radiationdirections.

In order to keep the extended radiation of the radiation diagram small,that is, in order to radiate at each angle energy of substantiallyidentical magnitude, the antenna would have to be made of dipoles eachof which radiates energy at an angle of :45 to its main radiationdirection, which is so small that it furnishes together with the energyof the neighboring dipole of the main radiation direction which isdisplaced by 90 a practically corresponding energy. In an antenna builtup of such dipoles, as much energy would be radiated at the angle of1:45 to the main radiation direction as in the four main directions.

The object of the invention is to provide an omnidirectional antennacomprising identical dipoles disposed in a common plane or level about acarrier, the dipoles being for good impedance matching shorter than fullwave, equipped with reflectors, the ratio of length of the dipoles tothe diameter thereof being such that the radiation characteristics isbroadened so that the energy radiated in the zone between neighboringmain radiation directions corresponds substantially to the energy of themain direction.

There are preferably disposed in one level four identical, for example,cylindrical dipoles arranged to define a rectangle. The radiationcharacteristic is then broadened with such dipoles in such a degree thatone fourth of the energy of the main radiation direction is radiated atan angle of -45 to the main radiation direction.

The ratio of length of the dipole to the diameter is suitably /25 andpreferably /25. The length of the dipoles is about to 35% shorter thanfull wave. The width of the radiation will then vary between that of afull wave dipole and that of a half wave dipole.

The invention will now be explained with reference to the accompanyingdrawings Figs. 1 and 2 showing in schematic plan views two embodimentsof omnidirectional antennas with their carriers.

In Fig. 1, there is a carrier or tower 1 provided with four identicallyconstructed cylindrical or rodshaped dipoles having respectively theelements 2-3, 4-5, 6-7

and 89 arranged to define the outline of the four sides of a rectangle.These dipoles are respectively mounted on reflectors indicated at 10,11,12 and 13, by means of arms 14 to 21 which are disposed in the zeropotential points of the individual dipole elements. The reflectors areheld by tubular members 22 to 25 containing the respective feed linesfor the dipoles. The length of the dipoles is about 20 to 35% shorterthan the operative wave-length in order to obtain good matching betweenthe input impedance of the dipoles and the wave impedance of the feedlines.

The spacing between the respective arms 14-15 and 1617 as well as 18-19and 20-21 which extend from the centers of gravity of the correspondingdipole ele ments is reduced, due to the considerable shortening of thedipole elements, thus reducing the concentration re sulting from thelateral spacing between the two points of the center of gravity of eachpair of dipole elements and thereby broadening the radiation diagram.

The broad band characteristic is with the specified ratio of lengths todiameter of the dipoles so favorable that the antenna is especiallyadapted for television purposes requiring particularly small mismatchingin a broad frequency range wherein f is the operating frequency and fthe mean frequency of the range.

The example illustrated in Fig. 2 shows an antenna comprising dipoleelements disposed in several planes or levels. The elements indicated infull lines lie in an upper level and the elements indicated in dottedlines lie in a level disposed underneath. The dipole elements of thedilferent levels are angularly displaced by about 22 so that the maximaof the radiation diagram of one level appears in the minima range of theradiation diagram of the other level. This angularly displaced arrayresults in further equalization of the radiated energy.

The anenna may be analogously provided with similarly angular displaceddipole elements in several additional levels. Several dipoles,preferably four dipoles of the same main radiating direction may then becoupled in a radiation unit for the purpose of matching their inputimpedance to the wave impedance of the feed line.

If a sturdy and stable tower or mast is used, there is the possibilityto dispose dipoles in a great number of superposed levels. Greatervertical concentration with very good matching in a broad frequencyrange will thereby be achieved than was heretofore possible with dipolesmay be employed for reinforcing the radiation in the desired sector.

Changes may be made within the scope and spirit of the appended claims.

I claim:

1. An antenna system comprising a plurality of individual structurallyidentical dipoles arranged in the general outline of a rectangle lyingin a common plane about a suitable carrier and having a reflector foreach dipole, each dipole comprising at least two colinear radiators,each dipole being for impedance matching shorter than full wave and thelength/diameter ratio of each dipole having a value lying between 10 and25, whereby the radiation characteristics of said dipoles is broadenedso that energy radiated in zones lying between neighboring 3principal-radiation directions corresponds substantially to 2,310,853Lindenblad Feb. 9, 1943 the energy radiated in the principal radiationdirections. 2,419,552 Himmel et a1. Apr. 29, 1947 2. An antenna systemaccording to claim 1, wherein 2,444,320 Woodward; June 29, 1948 thelength/diameterot said dipoles is between the values OTHER REFERENCESBrown: Institute of ;Radio Engineers Proceedings, vol. 33, 1945. PP.257-262.

Bailey: TV and other Receiving Antennas, 1950, Rider Inc., pp. 500-514.

References Citedinthe file .of this patent UNITED STATES PATENTS2,134,126 Hooven 1 25, 1938 10 Antennas (Kraus), published by,McGraw-Hill, 1950 2,163,770 Van Radinger June 27, 1939 (pp. 139, 142)2,238,904 Llgdenblad 1941 The A.R.R.L. Antenna Book," published byAmeri- ,2,298,'449 gBailey Oct. 13, 1942 can Radio Relay League, 1949,pp. 27, 28.

